1. Field of the Invention
Embodiments of the present invention relate to a battery pack.
2. Description of the Related Art
In general, primary batteries are batteries designed to be used once and discarded. Unlike the primary battery, the secondary battery may be recharged and may be used as the power source for various advanced electronic devices such as cellular phones, smart phones, notebook computers, camcorders, hybrid vehicles, electric vehicles, electric scooters and the like. In particular, lithium ion batteries are widely applied to the portable appliances because: (i) they have an operating voltage of 3.6 volts, which is about three times higher than a nickel-cadmium battery or a nickel-hydrogen battery, which are often used to power electronic equipment, and (ii) they possess high energy density per unit weight.
Since the lithium in a lithium ion secondary batteries generally exists in an ion state when the battery is used, lithium ion batteries are remarkably stable compared to metal lithium secondary batteries. However, since major components of lithium ion batteries (e.g., a negative electrode, electrolyte, etc.) are flammable, lithium ion batteries employ a highly sophisticated safety member to increase the battery stability, as compared to aqueous batteries. For example, lithium ion batteries may have a positive temperature coefficient (PTC) device mounted thereon, which is generally called a battery pack or a single pack.
When the temperature of a lithium ion battery having a PTC device mounted thereon exceeds a predetermined level, the PTC device has limitless electrical resistance. As a result. If the secondary battery reaches a high temperature state, the PTC device breaks the flow of charge/discharge current in order to allow the battery to cool. When the batter temperature decreases, the PTC device reversibly operates and the PTC device resistance is reduced, so that the battery may function properly.
However, when the PTC device is assembled with the secondary battery, an unwanted electric short-circuit between the secondary battery and the PTC device is likely to occur. For example, during assembling, a PTC device having negative polarity may be electrically shorted to a battery case having positive polarity. Thus, in order to prevent an unwanted electric short-circuit, many of additional components and process steps, including placing an insulating sheet between the secondary battery and the PTC device, have conventionally been employed, which is problematic.